Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by Sonia Etzwiler
The Nazca Plate
Situated in the southeastern Pacific Ocean, an oceanic tectonic plate called the Nazca plate shares boundaries that are both convergent and divergent. A convergent boundary is when two tectonic plates move toward each other and a divergent boundary is when two tectonic plates move away from each other. The Andes Mountains are the result of the subduction of the Nazca plate that lies below the South American continent. Subduction is the result of one plate that is usually lighter rising above a lower plate. The Nazca plate is located on multiple triple junctions, has three seamount chains, lies over four hotspots and is the cause of the Andean orogeny (Capitanio, 2011). This oceanic tectonic plate has gained much attention over the last half century due to the dangers it presents which are mainly earthquakes to the population of the west coast of South America.
The Nazca plate is the longest subduction zone in the world as it
stretches over 4.5 thousand miles and has produced the largest earthquake ever
recorded, the 9.5 Valdivia earthquake in 1960 (Perkins,
Aside from the damage this earthquake did to Chile, the resulting tsunami
affected other areas across the Pacific Ocean in Hawaii, Japan, the Philippines,
parts of New Zealand and Australia and the Aleutian Islands. Scientific studies
have contended that the Andes Mountains were created during a deliberate,
constant collision between the South American plate and the Nazca plate. Other
studies have offered that the mountain range formed much quicker due to a large
mass of rock breaking off beneath the mountains and sinking into the mantle
causing the continental crust to rise upwards at a much faster rate.
A converging boundary is the opposite of a divergent boundary and one will
normally see a converging boundary on a tectonic plate that is on the opposite
side of a divergent boundary. As a plate moves in one direction it collides with
the adjacent plate on its front end in a deep sea trench, while the trailing end
of the plate is being pulled and stretched (spreading) from the plate on the
other end at a mid-ocean ridge. Many times, volcanic activity can be detected at
converging boundaries due to plates crashing into each other.
When two plates collide, the leading edge if often deformed creating folding
rocks. The increase in crustal shortening actually increases the vertical
thickness of the lithosphere in the collision zone producing folds in the
mountains of the Andes (Hicks,
This constant action beneath the surface brings in seawater and while locked in
the crust of the ocean, the activity in the mantle produces magma that rises and
sometimes erupts at the surface (Forte,
Examples of this activity have been recorded in northern Chile and were
documented in 1993 and 2012 in Lascar.
The Andes Mountains have distinct topographic features which highlight a strong symmetry around the central region of the mountain range. The widest part of the range can be measured at 600 to 800 meters and are some of the highest elevations in the world. The symmetry of the Andes looks to be directly associated the symmetric features of the Nazca plate (Chlieh, 2011). It is suggested that a speedy subduction was the cause of this geographical feature that resulted in similar margins and deformations as those found deep in the Nazca plate. This is attributed to the decline of convergence rates to current day values which are results of increased pull of slab at these latitudes (Norabuena, 1998). Variations in the dominant plate pulling are directly connected to intense activity in the tectonic plates and motions feeding the rise in the Andes Mountains today.
Many of the largest earthquakes that have been recorded can be attributed to the
Nazca plates. The 1994 Bolivian earthquake and the 1960 and 2010 earthquake in
Chile are two of the strongest earthquakes ever recorded at a depth of over 300
meters and it was due to the subduction of the deep tectonic plates (Cisternas,
The zones where these plates are predominant are geologically complex and
produce numerous earthquakes from several tectonic processes that cause
deformation on the western edge of South America. This is due to crustal
deformation and ultimately mountain building in the Nazca plate. The Nazca plate
moves at an average of 15-17 centimeters a year and is colliding with the South
American plate creating this geographic anomaly that often results in the
creation of earthquakes, volcanoes and the formation of mountains.
The plate tectonics theory has been developed over the years to explain large scale motions of the rigid outer part of the Earth largely consisting of the crust and upper mantle. This theory supports how tectonic plates in South America produce geographic variances that cause earthquakes on the western coast of this country. Studying the rate of how these plates move and interact with other plates can assist in better understanding how earthquakes can change human structures but also how they change the earth in general.
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Chlieh, Mohamed, et al. "Interseismic Coupling and Seismic Potential Along the Central Andes Subduction Zone." Journal of Geophysical Research.Solid Earth 116.12 (2011)ProQuest. Web. 19 Apr. 2015.
Cisternas, Marco, et al. "Predecessors of the Giant 1960 Chile Earthquake." Nature 437.7057 (2005): 404-7. ProQuest. Web. 19 Apr. 2015.
Forte, A. M., et al. "Recent Tectonic Plate Decelerations Driven by Mantle Convection." Geophysical Research Letters 36.23 (2009)ProQuest. Web. 19 Apr. 2015.
Hicks, Stephen P., et al. "The 2010 Mw 8.8 Maule, Chile Earthquake: Nucleation and Rupture Propagation Controlled by a Subducted Topographic High." Geophysical Research Letters 39.19 (2012)ProQuest. Web. 19 Apr. 2015.
Norabuena, Edmundo, et al. "Space Geodetic Observations of Nazca-South America Convergence Across the Central Andes." Science 279.5349 (1998): 358-62. ProQuest. Web. 19 Apr. 2015.
Perkins, Sid. "Andes Rose rather Rapidly." Science News Jul 05 2008: 11. ProQuest. Web. 9 Apr. 2015.
"Trench-Parallel Flow Beneath the Nazca Plate from Seismic an." Science 263.5150 (1994): 1105. ProQuest. Web. 19 Apr. 2015.